Abstract
Heat-transfer experiments have been undertaken, using two different test facilities, on a wide variety of tube bundles arranged with warm gas flowing either across, or parallel to, the outside of the tubes and with cool water flowing inside them. The cross-flow tube bundles include radial-finned tubing in various ‘in-line’ formations, as well as a staggered arrangement of elliptical-section finned tubing. Of the two axial-flow tube bundles considered one is of radial-finned tubes and the other of longitudinal-finned tubes.
The gas-side heat-transfer and pressure-drop performance of all these tube arrangements are presented firstly in the form of the customary non-dimensional relations. The performances of the tube matrices are then compared using a number of utilization parameters, based on theoretical expressions of Colburn, covering not only the main factors involved in the cost of heat exchangers, but also the return of heat transfer for the gas-side pressure drop expended. By plotting graphs connecting these parameters, the relative merits of the various tube configurations in actual heat-exchanger applications can be assessed, and conclusions drawn as to the most suitable one to adopt for a particular purpose. A most useful graph is one connecting the parameters expressing the compactness of the tube matrix and the gas-side fluid resistance (see Fig. 15.8). Such a relation shows that the staggered cross-flow arrangement of elliptical tubes gives rise to reasonably compact matrices with only a moderate gas-side pressure drop. The cross-flow bundles of circular-section tubing, however, can result in extremely compact matrices having a high pressure loss, whilst the axial-flow configurations have exactly the opposite characteristics.
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